Current limit calculation for wind turbine control

Abstract

Systems and methods for determining current limits used in controlling wind turbine systems are provided. An example wind turbine controller identifies a largest current magnitude out of a first current magnitude, a second current magnitude, and a third current magnitude of a three phase power bus. The turbine controller averages the first current magnitude, the second current magnitude, and the third current magnitude to obtain an average current magnitude. The turbine controller determines a maximum current adjustment factor based at least in part on the largest current magnitude and based at least in part on the average current magnitude. The turbine controller adjusts a maximum current magnitude limit of the wind turbine by the maximum current adjustment factor to obtain an adjusted maximum current magnitude limit. The turbine controller controls the wind turbine based at least in part on the adjusted maximum current magnitude limit.

What is claimed is: 
     
       1. A method for controlling a power system having a multiphase output, said power system being electrically connected to a power grid having a plurality of phases of power, the method comprising:
 obtaining, by one or more control devices, data indicative of a first current magnitude of a first phase of a multiphase output, a second current magnitude of a second phase of the multiphase output, and a third current magnitude of a third phase of the multiphase output; 
 identifying, by the one or more control devices, a largest current magnitude out of the first current magnitude, the second current magnitude, and the third current magnitude; 
 averaging, by the one or more control devices, the first current magnitude, the second current magnitude, and the third current magnitude to obtain an average current magnitude; 
 determining, by the one or more control devices, a difference between the average current magnitude and the largest current magnitude to obtain a maximum current adjustment factor; 
 adjusting, by the one or more control devices, a maximum current magnitude limit of the power system by the maximum current adjustment factor to obtain an adjusted maximum current magnitude limit; and 
 controlling, by the one or more control devices, the power system based at least in part on the adjusted maximum current magnitude limit such that the multiphase output of the power system counter-acts imbalance among one or more of the plurality of phases of the power grid. 
 
     
     
       2. The method of  claim 1 , wherein controlling, by the one or more control devices, the power system based at least in part on the adjusted maximum current magnitude limit comprises:
 determining, by the one or more control devices, an adjusted maximum reactive current limit based at least in part on the adjusted maximum current magnitude limit; and 
 controlling, by the one or more control devices, the power system based at least in part on the adjusted maximum reactive limit. 
 
     
     
       3. The method of  claim 2 , wherein determining, by the one or more control devices, the maximum reactive current limit based at least in part on the adjusted maximum current magnitude limit comprises:
 squaring, by the one or more control devices, the adjusted maximum current magnitude limit to obtain a squared maximum current magnitude limit; 
 squaring, by the one or more control devices, a real current magnitude to obtain a squared real current magnitude; 
 determining, by the one or more control devices, a squared maximum reactive current limit based at least in part on the squared maximum current magnitude limit and based at least in part on the squared real current magnitude; and 
 determining, by the one or more control devices, a square root of the squared maximum reactive current limit to obtain the maximum reactive current limit. 
 
     
     
       4. The method of  claim 1 , wherein adjusting, by the one or more control devices, the maximum current magnitude limit comprises subtracting, by the one or more control devices, the maximum current adjustment factor from the maximum current magnitude limit to obtain the adjusted maximum current magnitude limit. 
     
     
       5. The method of  claim 1 , further comprising:
 scaling, by the one or more control devices, the maximum current adjustment factor by a scaling factor to obtain a scaled maximum current adjustment factor; 
 wherein adjusting, by the one or more control devices, the maximum current magnitude limit comprises adjusting, by the one or more control devices, the maximum current magnitude limit of the power system by the scaled maximum current adjustment factor to obtain the adjusted maximum current magnitude limit. 
 
     
     
       6. The method of  claim 1 , wherein a magnitude of the adjustment factor is determined based on a magnitude of the current imbalance. 
     
     
       7. A control system for a power system having a multiphase output, said power system being electrically connected to a power grid having a plurality of phases of power, the control system comprising:
 a selector that identifies a largest current magnitude out of a first current magnitude of a first phase of power, a second current magnitude of a second phase of power, and a third current magnitude of a third phase of power; 
 an average calculator that averages the first current magnitude, the second current magnitude, and the third current magnitude to obtain an average current magnitude; 
 a first summation node that subtracts the average current magnitude from the largest current magnitude to obtain a maximum current adjustment factor; 
 a second summation node that subtracts the maximum current adjustment factor from a maximum current magnitude limit of the power system to obtain an adjusted maximum current magnitude limit; 
 one or more control devices that control the power system based at least in part on the adjusted maximum current magnitude limit such that the multiphase output of the power system counter-acts imbalance among one or more of the plurality of phases of the power grid. 
 
     
     
       8. The control system of  claim 7 , wherein:
 the second summation node subtracts the maximum current adjustment factor from a maximum current magnitude limit of the power system to obtain an adjusted maximum current magnitude limit; and 
 the one or more control devices control the power system based at least in part on the adjusted maximum current magnitude limit. 
 
     
     
       9. The control system of  claim 8 , further comprising:
 a first multiplication node that multiplies the maximum current adjustment factor by a scaling factor to obtain a scaled maximum current adjustment factor; 
 wherein the second summation node subtracts the scaled maximum current adjustment factor from the maximum current magnitude limit of the power system to obtain the adjusted maximum current magnitude limit. 
 
     
     
       10. The control system of  claim 8 , further comprising:
 a reactive current limit calculator that determines a maximum reactive current limit based at least in part on the adjusted maximum current magnitude limit; 
 wherein the one or more control devices control the power system based at least in part on the maximum reactive current limit. 
 
     
     
       11. A wind turbine system, said wind turbine system being electrically connected to a power grid having a plurality of phases of power, comprising:
 a generator; 
 a rotor configured to rotatably drive the generator; 
 a turbine controller that:
 obtains data indicative of a first current magnitude of a first phase of power, a second current magnitude of a second phase of power, and a third current magnitude of a third phase of power; 
 identifies a largest current magnitude out of the first current magnitude, the second current magnitude, and the third current magnitude; 
 averages the first current magnitude, the second current magnitude, and the third current magnitude to obtain an average current magnitude; 
 subtracts the average current magnitude from the largest current magnitude to obtain a maximum current adjustment factor; 
 adjusts a maximum current magnitude limit of the wind turbine by the maximum current adjustment factor to obtain an adjusted maximum current magnitude limit: and 
 control the wind turbine based at least in part on the adjusted maximum current magnitude limit such that at least output of the wind turbine counter-acts imbalance among one or more of the plurality of phases of the power grid. 
 
 
     
     
       12. The wind turbine system of  claim 11 , wherein the turbine controller:
 subtracts the maximum current adjustment factor from the maximum current magnitude limit to obtain the adjusted maximum current magnitude limit. 
 
     
     
       13. The wind turbine system of  claim 11 , wherein the turbine controller:
 scales the maximum current adjustment factor by a scaling factor to obtain a scaled maximum current adjustment factor; 
 adjusts the maximum current magnitude limit of the wind turbine by the scaled maximum current adjustment factor to obtain the adjusted maximum current magnitude limit. 
 
     
     
       14. The wind turbine system of  claim 11 , wherein the turbine controller:
 determines a maximum reactive current limit based at least in part on the adjusted maximum current magnitude limit; and 
 controls the wind turbine based at least in part on the maximum reactive current limit.